#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 u_resolution;
uniform float u_time;

float box(in vec2 _st, in vec2 _size){
    _size = vec2(0.5) - _size * 0.5;
    vec2 uv = smoothstep(_size, _size + vec2(0.001), _st);
    uv *= smoothstep(_size, _size+vec2(0.001), vec2(1.0)-_st);
    return uv.x*uv.y;
}

float cross(in vec2 _st, float _size){
    return box(_st, vec2(_size, _size/4.0)) + box(_st, vec2(_size/4.0, _size));
}

void main(){
    vec2 st = gl_FragCoord.xy / u_resolution.xy;
    vec3 color = vec3(0.0);

    vec2 translate = vec2(cos(u_time), sin(u_time));
    st += translate * 0.3;

    color = vec3(st.x,st.y,0.0);
    color += vec3(cross(st, 0.25));

    gl_FragColor = vec4(color, 1.0);
}
